The invention relates to a shut-off apparatus for the charging device of a pressure vessel, especially for the storage of cryogenic liquefied gases, having a shut-off valve with a valve housing and a valve body stressed by a closure spring which, in order to charge the pressure vessel, can be brought into the open position against the force of the closure spring, having an apparatus for locking the valve body in the open position of the valve and having a release apparatus subjected to the action of the vessel pressure, which causes the apparatus to release the lock if a predetermined threshold vessel pressure is exceeded.
An essential aspect of the design of shut-off apparatuses for the charging device of a pressure vessel is the reliable avoidance of excess pressures when charging the pressure vessels.
The shut-off apparatuses must first offer a maximum level of safety and secondly exclude as effectively as possible any manipulation or switching-off of the shut-off apparatuses. In particular, an independent control of the shut-off apparatus which is as isolated as possible from external influences must be guaranteed.
DE-OS 21 56 068 has disclosed a shut-off apparatus controlled by an independent medium for avoiding excess pressures in a gas or fluid line with a shut-off valve, in which the valve body is equipped with a resilient means in the form of a closure spring to generate a force in the closed position, an apparatus for locking being provided in the form of a locking lever and an assigned projection on the valve stem, this locking apparatus permitting the locking of the shut-off valve in the open position against the force acting towards the closed position, and this locking apparatus comprising release apparatuses for releasing the locking apparatus in the event that the pressure rises above or falls below a predetermined maximum or minimum pressure.
DE 196 50 560 A1 has likewise disclosed a shut-off apparatus for the charging device of a pressure vessel, in which the release apparatus possesses a bellows subjected to the vessel pressure with a switch rod attached thereto which pivots the locking apparatus of the valve body, designed as a closure lever, out of the locking position into the release position if vessel pressures exceed or fall below vessel threshold pressures.
In the known shut-off apparatuses for the charging device of a pressure vessel it is a problem, depending on the surroundings and the existing safety regulations, that the cryogenic gas is blown off during release and also after release. In some circumstances, the place of escape has to be moved by the costly piping of the gas into low hazard potential areas. It is also advantageous if the control line between the pressure vessel and the release apparatus possesses a narrow cross section xe2x80x94as is customary in signal lines.
Starting from this state of the art, therefore, the object of the invention is to provide a release apparatus for a shut-off apparatus which permits the release of the shut-off apparatus with little or no blow-off of the cryogenic gases conveyed.
The object derived and described above is achieved, according to the invention in that the release apparatus possesses a cylinder, a piston and a piston rod, in that a medium-permeable annular gap is provided between piston and cylinder, in that the piston rod acts on the apparatus to release the lock, in that the cylinder possesses an overflow valve on one side of the piston which opens when the threshold vessel pressure is reached, in that, when the overflow valve is open, the cylinder is in flow connection with the pressure vessel on one side of the piston and is in flow connection with a reference pressure volume, preferably the ambient atmosphere, on the other side of the piston.
With the improved release apparatus of the shut-off apparatus according to the invention, the release of the locking apparatus as a precisely reproducible step function is guaranteed in that the switching forces are abruptly boosted via a pneumatic booster at the start of the overflow valve opening operation, which can be precisely predetermined. In the shut-off apparatus according to the invention, this abrupt boost is guaranteed by simple pneumatic means and not by precision engineering with the disadvantages of costly production and adjustment. As soon as the overflow valve opens, a differential pressure arises across the annular gap between piston and cylinder and, by acting on the piston surface, guarantees a pneumatic force boost to release the shut-off apparatus.
As a result of the fact that, according to a first alternative embodiment of the shut-off apparatus according to the invention, an unobstructed control line opens into the cylinder on one side of the piston to create the flow connection to the pressure vessel and that the cylinder is connected to the overflow valve on the other side of the piston, the vessel pressure prevails in the entire cylinder when the overflow valve is shut. If the vessel pressure exceeds the vessel threshold pressure, the overflow valve opens, as a result of which, because of the relatively narrow annular gap, a lower pressure arises on the side of the piston opposite the control line than on the other side of the piston, which in turn results in the piston being subjected to a high force towards the side of the piston remote from the unobstructed control line to release the shut-off apparatus.
As an alternative to the embodiment of the shut-off apparatus according to the invention just described, a control line opens into the cylinder on one side of the piston via the overflow valve to create the flow connection to the pressure vessel and the cylinder is in unobstructed flow connection with the reference pressure volume on the other side of the piston. In this alternative version, the cylinder is under the pressure of the reference pressure volume when the overflow valve is shut. As soon as the overflow valve opens, in this alternative version, the pressure on the side of the piston facing the control line rises rapidly because of the narrow annular gap, so that the pressure difference between the two sides of the piston pneumatically boosts the opening of the overflow valve.
The effect is that, in both alternative versions, the embodiment according to the invention ensures that the piston rod of the release apparatus is abruptly accelerated at the moment when the overflow valve begins to open and thus acts on the apparatus by way of a single-step function to release the locking.
In order to bring about a defined initial state and to restore the release apparatus automatically when necessary, it is advantageous that, according to another embodiment of the invention, the piston rod is subjected to force via a spring towards the side of the piston facing the control line.
The second alternative embodiment of the release apparatus described is advantageously further developed in that the end of the piston rod facing the control line bears the sealing element of the over flow valve. This guarantees that the piston rod of the release apparatus, which is subjected to force, forms the overflow valve together with the sealing element and the valve seat arranged at one end of the cylinder. As a result, the number of components is reduced by comparison with an embodiment with a separate overflow valve.
If it is desired, in the case of the second alternative embodiment, that the release apparatus should not be restored automatically when the vessel pressure drops below the vessel threshold pressure, this can be guaranteed in that the cylinder and the piston on the side remote from the control line interrupt the flow connection to the reference pressure volume in the end position of the piston movement. As a result of the interruption of the flow connection to the reference pressure volume, the pressure in the cylinder is statically held at the vessel pressure, since the gas cannot flow out via the flow connection to the reference pressure volume. This static pressure difference then ensures that the piston cannot be restored automatically.
For controlled restoration, the shut-off apparatus according to the invention is further developed in that the cylinder is in flow connection with the reference pressure volume via a valve on the side facing the control line. Via such a valve, which may for example be manually actuated, it is possible to reduce the pressure on the side of the piston facing the control line to such an extent that a resetting of the piston and hence of the release apparatus becomes possible.
The two alternative embodiments of the release apparatus described are advantageous in that the control line does not require any large cross sections and in that little or no blow-off of the gases or media take place at the release apparatus. In particular, in the embodiment of the second alternative version, in which the flow connections to the reference pressure volume are interrupted by interaction of cylinder and piston, only a small quantity of gas or medium enters the reference pressure volume meaning, in particular, the environment.
There are many possible ways of embodying and developing the shut-off apparatus according to the invention for the charging device of a pressure vessel. In this connection, reference is made by ways of example first to the patent claims dependent on Patent claim 1 and secondly to the description of examples of embodiment of the shut-off apparatus according to the invention for the charging device of a pressure vessel in conjunction with the drawing. In the drawing: